This invention relates to an actuator for fluid pressure-operated motors, particularly pneumatically operated setting devices.
Setting devices of the above-outlined type, particularly power cylinders, control cylinders, valves or the like have been used for a long time in measuring and control systems for measuring pressure, temperature or material quantities, for electromechanical processes, for indicating and controlling contents in silos and containers, for throttle devices, vane guides, flaps, etc.
In the above applications, the setting devices are in general coupled through a switch valve with the supply circuit (hereinafter also referred to as pressure source) of the pressurized medium. In such an arrangement it is necessary that the setting device (for example, a double-acting power cylinder) be connected to the pressure source by means of at least two conduits. Each of these two conduits serves for separately pressurizing the two oppositely oriented radial end faces of the piston disposed in the cylinder and/or for the introduction and withdrawal of the pressure medium which is usually a gas but which may also be a liquid.
Systems and devices of the above-outlined type are disclosed, for example, in French Pat. Nos. 2,115,506 and 2.201,406, U.S. Pat. Nos. 3,727,639 and 3,754,400 as well as in the German Laid-Open Application (Offenlegungsschrift) No. 1,916,266.
It is a common characteristic of all of the above known systems, devices or circuits that the setting device or, as the case may be, the setting members are in direct communication with the pressure source (such as a pump or a fan or the like) by a separate supply conduit and a return conduit or by two pressure conduits. The supply and return conduits, together with the setting device and the source for the pressure medium form a closed circuit, as it may be observed, for example, in French Pat. No. 2,115,506 (FIG. 1, conduits 30 and 32).
In practice, pneumatically operated setting components are, for operational reasons, in most cases disposed at a significant distance from the main circuit of the pressure medium.
Particularly in case of systems which operate with a plurality of pneumatically driven setting members, such as measuring or control centers of refineries, steam generating or cooling water systems in power plants, large capacity silos, nuclear plants, aerating systems in schools, storehouses, etc., the pressurized fluid is almost always drawn from a main supply network and the setting members are in most cases disposed at locations which are not easily accessible. For these reasons, there are needed substantial amounts of conduits for the purpose of bridging, by means of a double conduit, the distance, for example, from the main pressure network through the control station to the setting member. For this reason, plants like oil refineries, petro-chemical plants, cold storage buildings, large-capacity heating arrangements and the like very often need hundreds or even thousands of meters of double conduits.
Apart from the need for a substantial material and labor input with regard to such double conduits, the probability that defects and breakdowns occur along the conduits is doubled. This substantial risk, coupled with additional required maintainance projects thus have to be considered as true disadvantages in the systems of the above-outlined type and consequently are to be looked upon as an operational problem of prime importance.
If, for example, in a system according to French Pat. No. 2,115,506 there are arranged, adjacent to one another, four setting members at a location which is accessible only with difficulty, according to the presently known methods -- despite the proximity of the setting members -- all four setting members are separately connected with the supply network for the medium by means of their own dual conduit.
Since the supply network (main conduit) for the pressurized fluid is supported in most cases on a pipe or conduit bridge which almost always extends centrally through the hall or centrally with respect to the system disposed in open air and since between the supply conduit and the setting member, apart from an energizing element, in most cases there is a central switching station, the dual conduits serving the system tend, in their totality, to create visual confusion.